As I recall, a SUBST command goes through a mapping (since the command-line doesn't support UNC names):
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USE H: \\SERVER\SHARE
SHELL '%comspec% /c SUBST U: H:\@userid'
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UPDATE: I tried subst on an UNC name and it does map but the drive is not accessible.

[ 10 August 2001: Message edited by: Fuentez ]